Our ILA Round Table workshop was recorded today with Dr. Louis Landesman acting as leading expert on fertilization tips for duckweed production. It’s an hour long but one of the best hours you could spend if you were really interested in growing duckweed for urban farming or commercial purposes.
Thanks, Louis. Wonderful job!
A sunny window and spring green loveliness of happy duckweed make up for the damp chill of March. This duckweed was grown primarily on aquarium water from my goldfish with a bit of trace pond muck for micronutrients. It is doubling every three days at present. Another month and sunlight intensity will move that growth rate up to nearly a doubling every one and a half days.
Photo taken by my good friend, Linda King.
Duckweed – a future crop plant for India?
Do you know the water plant “duckweed”? Even when you have not yet heard the word, we are sure you know it. Have you ever seen little green plants floating on the water surface of ponds, lakes or small channels? With high probability – these are duckweeds. They look very tiny and seem to be unwanted but they might be potential contributors in solving some of the most important problems of mankind, not only in India.
Duckweed–a future crop plant for India?
The world population crossed the 7 billion mark almost two years back. It is predicted that by 2050 (which is not so far away!) it will be 9.6 billion. India has 1.21 billion people just behind the country with the largest population, China (1.34) but will soon be at the top. This has serious consequences concerning the worldwide availability of food, energy and fresh water. The larger number of people in future will also have higher demands per person concerning the food quality. Energy supply is getting more and more difficult as the development since last 200 years in the industrialised western countries is based on terrestrial stocks like coal and gas. It is clear now that energy supply on a long range has to be sustainable and cannot base unlimited on coal, oil, gas or atomic power. Moreover, burning coal and oil contributes to the increase of the global temperature with adverse effects on agriculture and water supply. At the moment, the availability of fresh water is already one of the most serious problems as cleaning of waste water or its regeneration in nature is not anymore in tune with the accumulating amount of municipal or even industrial waste.
The name of this family of plants in English, “duckweed”, tells us already a lot about the importance of these seemingly inconspicuous plants. Have you ever seen ducks or other water fowls eating duckweed? Evidently they love it. This explains the first part of the name. The second part suggests that these plants grow like a weed, i. e. very fast. This is indeed the case. We have to talk about is later.
Shall we first have a closer look at how duckweeds look like or how they grow? This is important when we think of duckweed as a potential crop plant. We have to learn that duckweed is not a specific, single plant but a whole plant family – although a small one consisting of only 37 species. In India four of them are very common. They are scientifically named Spirodela polyrhiza, Landoltia punctata, Lemna aequinoctialis, and Wolffia globosa. There are approximately eight more species but these are rather rare in India. The four common species are very different, e.g. in size. Single plants of Spirodela polyrhiza have a size of approximately 1.5 cm – and this is the largest duckweed, also called giant duckweed. Such plants are often connected to 2 or even 10 other plants and then the whole colony looks much larger. The size of Wolffia globosa is below 1 mm, often are two plants (mother and daughter) connected to each other. The other two species are between Spirodela polyrhiza and Wolffia globosa in size, less than 1 cm.
Duckweeds are flowering plants. The flowers are tiny and hardly seen without a magnification glass. Last year on our field trip to Madhya Pradesh, we saw a lake full of flowering Lemna aequinoctialis. However, such a view is very rare. Normally, these plants propagate without flowering. This is termed vegetative propagation: the younger plants (daughters) come just out of a hidden pocket of the older plant (mother). The daughters which are still connected to the mother plant develop granddaughters inside them and even further generations. This is most probably the secret of the very fast growth of duckweed. The precise growth rate depends on the duckweed species, temperature, light conditions and the composition of the pond water. As an example, plants can double their number in 2 days or even less. Try to count for a few days: Let’s start with 10 plants. After two days there are 20 plants, after 2 more days 40 plants and then 80 plants. Of course this will not continue forever. When the space is limiting then the growth is limited. But can you see the potential of duckweed with their very fast growth? This is not only in the scientific laboratory. Meanwhile, also first outdoor results are known. For the two common species in India, Spirodela polyrhiza and Landoltia punctata, the harvest dry weight yields between 24 and 54 t ha-1 yr-1 and 69 and 117 t ha-1 yr-1, respectively, are known. This can be compared with common land crop plants in agriculture. The comparable value for sugar cane is 23 t ha-1 yr-1, the highest in Ethiopia in 2010 was 41 t ha-1 yr-1. The best national yearly yields of sugar beet, potato, maize, rice and wheat grains in the United States were 17.1, 11.1, 9.6, 7.6 and 2.9 t ha-1 yr-1, respectively (Source: USDA). This shows that duckweeds can indeed be used to produce more biomass per area of cultivation than any land-based crop. Moreover, the cultivation of duckweed does not need fertile land. Duckweeds can be produced in aquaculture wherever the other required factors are available, also on barren land.
What are the other required factors? Duckweeds have an optimal growth temperature of around 28 C. At temperatures around 35 C, growth is almost completely stopped. Together with the requirement for sufficient sun light these requirements are almost ideally fulfilled in many areas of India throughout the year, except in the high altitudes. Consequently, duckweed can be found everywhere in India from Kerala to Jammu and from Gujarat to West Bengal.
We have not yet mentioned the requirement for fertilizers. In the present day agriculture, often large amounts of fertilizers are sprayed on the soil. A part of it finally is washed out and contaminates surface or even ground water. This is quite different in the aquaculture of duckweeds. Duckweeds can grow very well on waste water. Waste water contains a large amount of chemicals which are nutrients for plants, e.g. phosphate and nitrate. Growing plants need to take up nutrients to support their growth. Instead of using large amounts of fertilizers which unavoidably also contaminate water, duckweed take nutrients from contaminated waste water and clean it this way. One precondition is: waste water must not contain too much toxic compounds like herbicides or pesticides or chromate as it sometimes is the case in industrial waste water. Such toxic compounds must be removed before they reach surface or ground water as it is dangerous for humans anyway.
Thus, we can produce very effectively huge amount of biomass from aquaculture of duckweed and during duckweed cultivation the waste water can be cleaned. The next important question arises: What can be done with this duckweed biomass? What are the harvested duckweeds good for?
To learn about these facts you will have to wait for our next article!!!
Views expressed by PD Dr Klaus-J Appenroth, University of Jena, Germany (Klaus.Appenroth@uni-jena.de) and Dr K Sowjanya Sree, AIMT, Amity University, Noida, UP, India (email@example.com)
Duckweed is popping up here and there in my ponds. Woo hoo! Spring is FINALLY here!
So far, I have harvested samples of Lemna turionifera, Spirodela polyrhiza turions and Wolffia. All are tucked nicely under gentle flourescent lights in warm temps and are acclimatizing to their new surroundings. It has been a struggle to keep my test samples warm enough in an unheated lab in an unheated warehouse so I fashioned a plastic “blanket” around and over said growing chamber and plugged in a space heater. I designed the plastic blanket sort of like a skort so I could gain access easier without losing all the heat every time I opening it up. Works great!
I took the photo below with my cell phone and a 10x magnifying lens. It shows what newly emerged S. polyrhiza looks like before it begins budding. The Wolffia is so tiny, I didn’t even know it was there until I looked at it under a microscope. Wolffia- the world’s smallest flowering plant… Gotta love it.
Note: Just so you know what a fanatic I am about getting early spring samples, I got my pickup mired down into muck up to my axles not once but TWICE during this bioprospecting venture. I had to walk 1/2 a mile to the nearest house and my good buddy, Joe Currin of Mayfield pulled me out twice before I was back on solid ground. It was worth it. :)
So I lied.
Our third ice storm of the year hit two days ago. My son’s car is stuck in the snow and my pickup battery is dead or I’d pull him out. Instead, necessity demands that he invent new ways to dig his car out sans a shovel. Should be interesting.
I am holed up next to my WFO and enjoying the gentle warmth.The kids are getting out of school again for the third entire week this winter. That pretty much wraps up them having much of a decent summer vacation.
And what of my plans for bioprospecting duckweed this week?
Sigh… All ponds are once again covered with a layer of ice and six inches of new snow. Spring duckweed sampling will have to wait. Am keeping myself busy with securing lab equipment and designing research studies. Keeps me out of trouble.
If you’ve been following my story for the past couple of years, you’ll know I have the tendency to go the DIY route as often as possible. I get a lot done on a nickel but spend a heck of a lot of time on construction that probably could be better spent soliciting investors or finishing that duckweed manual. So it goes…
For now, I’ll simply use folding tables for work space and drag in a small desk. When it gets hot, I’ll put an old window AC unit in the wall to the right of the upper cabinets.
My kids will be thrilled that I am moving all my lab stuff out of our home kitchen. One of my daughters looked at this picture today and muttered, “When is OUR kitchen going to look that finished?”
Ouch. She is right. My problem, other than procrastination, is that my tools are there and I need them here. End of story.